Hydration process of fly ash blended cement pastes by impedance measurement

•Hydration of high-dosage fly ash blended cement pastes is evaluated.•Four hydration stages are identified.•Gismondine is found in the zeolite formation stage. This study focuses on the early-age hydration development in fly ash blended cement pastes. The characteristic features in different hydration stages and the evolution of zeolites phase, viz., gismondine, are identified in high-dosage fly ash blended cement-based materials using the innovative non-contact impedance measurement (NCIM), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), heat evolution test and pore solution analysis. It is found that the zeolite formation stage is comparatively distinct at the late hydration period. Besides, the influence of fly ash dosages in cement pastes on setting time and compressive strength are further examined.